The C4 Explosive is a standard military plastic explosive with built-in detonator, and is a classic demolition tool. With an improved composition, the C4 is extremely effective against breaching obstacles or demolition of large structures. Once placed, the device must be armed before it can be detonated remotely with the clacker.
In Killzone 2's Multiplayer, the C4 is a sticky explosive, and the Saboteur's secondary badge. When spawned, you are given three of them, and once thrown they stick to anything, including enemies and friendlies. New explosives become available for you to use once the old ones explode. You can also manually blow up the C4 by throwing a grenade or shooting them.
One single explosive isn't enough to kill an enemy with full health, so it is highly recommended to place them on groups to ensure their efficiency.